Heat Exchangers

ABSTRACT

A heat exchanger  11  for use as a cross flow radiator for an engine cooling system has a heat exchanger matrix  12 , header tanks  13, 14  and a side plate  16  arranged at the upper of a pair of opposite side edges  16, 17  of the matrix  12 . The matrix  12  has tubes  18  which extend between tanks  13, 14  and cooling fins  19 . A restrictor plate  21  arranged on side plate  16  restricts air flow past fin  19 A. Restrictor plate  21  may have cut out gaps or castellations  22 . This reduces heat transfer through the fins above the uppermost tube  18 A allowing for a more even temperature distribution, which reduces stress from thermal expansion.

FIELD OF INVENTION

The invention relates to heat exchangers; in particular to enginecooling system radiators.

BACKGROUND OF THE INVENTION

Heat exchangers, particularly those used as engine cooling systemradiators, often have a generally rectangular heat exchanger matrix, aninlet header tank and an outlet header tank each at a respective one ofone pair of opposite side edges of the matrix and a pair of side plateseach arranged at an a respective one of the other pair of opposite sideedges of the matrix. The matrix has a number of tubes extending in aparallel array between the tanks to provide a path for liquid coolant toflow from one tank to the other. Cooling fins are arranged betweenadjacent pairs of tubes and between each side plate and the adjacenttube such that in use air flows between adjacent pairs of tubes andbetween each side plate and its adjacent tube.

A problem with the heat exchangers described above is that the tubeswhich are adjacent the side plates may be overcooled since it is commonto provide the same size and type of fins between these components asare used between adjacent pairs of tubes. The fins situated between aside plate and an adjacent tube can conduct heat away from one tube onlywhile the fins situated between adjacent pairs of tubes have to conductheat away from two tubes. This overcooling can be particularlynoticeable if the heat exchanger is arranged with the tubes horizontaland the header tanks vertical (a so-called cross flow radiator). Wherethere is a relatively low rate of flow of liquid coolant and high airflow such as is encountered in a motor vehicle during gentle open roadcruising, the hotter coolant tends to rise by convection to the uppertubes. The difference in temperature between the uppermost tube (i.e.,the one adjacent the uppermost side plate) and the next tube down canlead to stress cracking of the tubes or tube to header tank joint with asubsequent loss of coolant.

SUMMARY OF THE INVENTION

According to the invention, there is provided a heat exchanger having agenerally rectangular heat exchanger matrix, an inlet header tank and anoutlet header tank each at a respective one of a pair of opposite sideedges of the matrix and a pair of side plates each arranged at an arespective one of the other pair of opposite side edges of the matrix.The matrix has a plurality of tubes extending in a parallel arraybetween the tanks to provide a path for liquid to flow from one tank tothe other and cooling fins arranged between adjacent pairs of tubes andbetween each side plate and the adjacent tube such that, in use, airflows between adjacent pairs of tubes and between each side plate andthe adjacent tube. The heat exchanger also has heat transfer restrictorsto restrict the transfer of heat from the tube adjacent one of the sideplates to the air flow between the one side plate and the tube.

In one embodiment, the heat transfer restrictor has a restrictor platearranged on at least one of the side plates to restrict the flow of airbetween the one side plate and the adjacent tube.

In another embodiment, the restrictor plate has a blanking plate havingcut out gaps or castellations. The blanking plate, in use, blocks theflow of air between the side plate and the adjacent tube over part ofits length and allowing air to flow through the gaps over the remainderof its length. Alternatively, the restrictor plate has a blanking platewith perforations to restrict the flow of air between the side plate andthe adjacent tube or a strip of constant width that extends the lengthof the side plate and over part of the gap between the side plate andthe adjacent tube to leave a narrow slit for air to pass through. Therestrictor plate may be attached to or form part of a cooling fan cowl.

An advantage of the present invention is that the heat transfer ratefrom the plurality of tubes is more uniform so that the temperaturesdifferences are lessened. Consequently, the stresses on the radiator areless, thereby preventing cracking failures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example and with referenceto the accompanying drawings, in which:

FIG. 1 is a perspective view of part of a vehicle heat exchangeraccording to the invention; and

FIG. 2 is a perspective view based on FIG. 1 but to a larger scaleshowing part of a conventional vehicle heat exchanger according to theprior art.

DETAILED DESCRIPTION

The vehicle heat exchanger 11 shown in FIG. 1 is a cross flow radiatorfor an engine cooling system. It has a generally rectangular heatexchanger matrix 12, an inlet header tank 13 and an outlet header tank14, each at a respective one of one pair of opposite side edges 15 ofthe matrix 12. A side plate 16 is arranged at the upper of the otherpair of opposite side edges 17 of the matrix 12, there being acorresponding side plate 16 arranged at the opposite, lower, side edge(not shown). The matrix 12 has a number of tubes 18 which extend in aparallel array between the tanks 13, 14 to provide a path for liquidcoolant to flow from one tank to the other. Cooling fins 19 are arrangedbetween adjacent pairs of the tubes 18 and between each side plate 16and the adjacent tube such that in use air flows not only betweenadjacent pairs of tubes but also between each side plate and itsadjacent tube. As is best seen in the conventional heat exchanger shownin FIG. 2, the fins 19 are in the form of a flat strip bent into acorrugated or serpentine formation with the crests bonded to the tubesto aid conduction. As a production expedient, the fins 19 are identicalthroughout the matrix 12 such that the fins 19A between each side plate16 and its adjacent tube 18A are the as fins 19B as those betweenadjacent tubes 18A and 18B.

In FIG. 2, tube 18A is cooled by fins 19A and 19B. Fin 19B is sharedbetween tubes 18A and 18B. Tube 18B is cooled by fins 19B and 19C. Both19B and 19C are shared between two tubes: 18A and 18B share fin 19B and18B and 18C share fin 19C. Because tube 18A has one fin that is notshared, fin 19A, and one fin that is shared, fin, 19B, it receivespreferential cooling compared to tube 18B in which its two adjacent finsare shared fins. Consequently tube 18A, which is an edge tube, runscooler than interior tubes, such as tubes 18B and 18C. The drawback ofunequal heat transfer rates is that the edge tube 18A runs colder thanits adjacent tube 18B so that the different expansion rates createstresses that can result in structural failure.

In the heat exchanger shown in FIG. 1, a restrictor plate 21, accordingto an aspect of the present invention, is arranged on the upper sideplate 16 to restrict the flow of air past edge fin 19A, i.e., the finbetween side plate 16 and uppermost tube 18A. Restrictor plate 21 isshown as being attached to side plate 16 (e.g. by adhesives, riveting orby welding). However, in an alternative embodiment, restrictor plate 21is formed as part of side plate 16. In yet another alternativeembodiment, restrictor plate 21 is part of or attached to a fan cowl ofany known type, e.g. as shown in EP0108479B1. The restrictor plate 21 isa rectangular blanking plate which blocks the flow of air which wouldpass through the space between the side plate 16 and the uppermost tube18A. As shown in FIG. 1, restrictor 21 has cut-out gaps.

Other forms of openings can be arranged in the restrictor plate 21, e.g.circular holes or perforations. Alternatively, there are no openings assuch but instead the restrictor plate 21 is a plain rectangular strip ofconstant width that extends horizontally the length of the side plate 16and vertically over part of the gap between the side plate and theadjacent tube to leave a narrow slit for air to pass through.Alternatively, the restrictor plate is arranged on the downstream(relative to the airflow) side of the side plate 16. In yet anotheralternative, a restrictor plate is placed on both sides, e.g. formingthe sides of a channel section. Indeed, other heat transfer restrictorsmay be provided to restrict the transfer of heat from the tube adjacentthe side plate to the air flow between the side plate and the tube. Forexample, the fins 19 may be reduced in number or in length to reducetheir ability to transfer heat from the tube to the airflow.

Although restrictor plate 21 and its variations and equivalents havebeen described in relation to the top side plate of a cross flowradiator, a flow restrictor can also be used on the lower side plate oron the side plates of a vertical flow radiator. However, the problem ofthermal expansion is usually much less concern in these areas. Otherheat exchangers may also benefit, e.g. air conditioning condensers.

1. A heat exchanger, comprising: a generally rectangular heat exchangermatrix; an inlet header tank at one edge of said matrix; an outletheader tank at a second edge of said matrix, said second edge beingopposite from said first edge; first and second side plates on third andfourth edges of the matrix; a plurality of tubes extending in a parallelarray between said inlet and outlet header tanks to provide a path forliquid to flow between said tanks; a plurality of interior cooling finsarranged between adjacent pairs of tubes; an edge cooling fin arrangedbetween said first side plate and said first side plate's adjacent tube;and a restrictor placed in adjacent said edge cooling fin.
 2. The heatexchanger of claim 1, further comprising: a second edge cooling finarranged between said second side plate and said second side plate'sadjacent tube; and a second restrictor placed adjacent said second edgecooling fin.
 3. The heat exchanger of claim 1 wherein said restrictor isa plate with cut-outs.
 4. The heat exchanger of claim 1 wherein saidrestrictor is a plate which occludes a portion of said edge fin.
 5. Theheat exchanger of claim 3 wherein said restrictor is of nearly constantwidth.
 6. The heat exchanger of claim 1 wherein said restrictor occludesan upstream side of said edge fin.
 7. The heat exchanger of claim 1wherein said restrictor occludes a downstream side of said edge fin. 8.The heat exchanger of claim 1 wherein said restrictor occludes anupstream side of said edge fin, said heat exchanger further comprising:a second restrictor occluding a downstream side of said edge fin.
 9. Theheat exchanger of claim 1 wherein the restrictor is part of a coolingfan cowl.
 10. The heat exchanger of claim 1 wherein said restrictor isattached to said first plate.
 11. The heat exchanger of claim 10 whereinsaid restrictor is attached to said first plate by at least one of:welding, gluing, crimping, and riveting.
 12. The heat exchanger of claim10 wherein the heat exchanger is a cross-flow radiator.
 13. A cross-flowradiator, comprising: a generally rectangular heat exchanger matrix; aninlet header tank at one edge of said matrix; an outlet header tank at asecond edge of said matrix, said second edge being opposite from saidfirst edge; first and second side plates on third and fourth edges ofthe matrix; a plurality of tubes extending between said inlet and outletheader tanks to provide a path for liquid to flow between said tanks; acooling fin arranged between said first side plate and said first sideplate's adjacent tube; and a restrictor plate placed adjacent saidcooling fin.
 14. The radiator of claim 13 wherein said restrictor plateis attached to said first side plate occluding an upstream side of saidcooling fin.
 15. The radiator of claim 13 wherein said restrictor plateis attached to said first side plate occluding a downstream side of saidcooling fin.
 16. The radiator of claim 13 wherein said restrictor plateis part of a cooling fan cowl.
 17. The radiator of claim 13 wherein saidrestrictor plate has perforations so that only a portion of thecross-sectional area of said cooling fin is occluded.
 18. The radiatorof claim 13 wherein said restrictor plate is narrower than the coolingfin width so that a portion of said cooling fin cross-sectional area isoccluded.
 19. The radiator of claim 13 wherein said cooling fin is anedge cooling fin and along its length has a first number of waves, theradiator further comprising: a plurality of interior fins having asecond number of waves along their length, wherein said second number ofwaves is greater than said first number of waves.